Methods for generating inert gases (such as, nitrogen gas streams or of primarily nitrogen gas stream in combination with other inert gases, such as carbon dioxide, are used in many different industrial applications. For example, an inert gas or an inert gas mixture can be used to prevent instantaneous combustion or explosive ignition, in limiting corrosion and oxidation (for example, as in inert gas blanketing), in semi-conductor manufacturing processes, or in specialized heat treating applications.
Inert gases can be used for inerting the ullage in large oil tanks or other types of containers employed to store or deliver combustible fluids. In these cases, an inert gas or an inert gas mixture is used to fill the head space in the tanks prior to filling or during off-loading of the tanks. This precaution is employed to prevent combustion or explosions within the tanks due to the initial presence or influx of air during the filling and/or emptying process.
Inert gases have been used to facilitate the removal of crude oil from semi-depleted oil wells. Injection of the inert gas into these wells causes some of the gas to dissolve within the residual oil reserves due to substantial overpressure created by the gas deep within the wells. The subsequent increase in reservoir pressure and/or reductions of well fluid column weight while flowing is capable of bringing large quantities of additional oil to the surface. In other cases, multiple inert gas injection sites, surrounding a centralized non-pressurized extraction site, may be simultaneously pressurized with an inert gas or mixture of inert gases. In this scenario, circumferential gas pressure alone will tend to force residual quantities of subsurface oil to flow to the surface region of a well through the centralized non-pressurized extraction site.
In order for a gas to be used as an inert gas in applications where the prevention of combustion and/or oxidation is critical, the oxygen content in the inert gas must be sufficiently reduced to a level that will not sustain fire or explosion. For example, inert gases having oxygen contents of less than about 2.0 percent by volume are preferred for inerting the head space in oil tankers.
High purity, cryogenic grade liquid nitrogen, which can be vaporized to produce high purity gaseous nitrogen, is usually about 99.99 percent pure (at least). This grade of nitrogen is typically employed in various inerting processes, including some of the applications already mentioned herein.
Cryogenic grade liquid nitrogen is generally made in large air separation plants, transported in the liquid state to a point of use location, and employed either directly as a liquid or as a gas after vaporization. Argon is another type of inert gas which is produced and employed similarly. The generation, transportation, and vaporizing of high purity cryogenic grade inert gases is very costly.
Some existing methods utilized to produce inert gas on-site entail conventional membrane systems employed to produce gaseous nitrogen from air. These kinds of systems typically produce gaseous nitrogen onsite with purity levels on the order of about 90 to 93 percent by volume. However, these systems are quite expensive due to high energy requirements and achieve relatively low nitrogen gas flow rates at high purity production levels.
An alternative way to produce an inert gas stream is through the combustion of an organic fuel. For example, the product gas stream produced as a result of any combustion process involving the burning of gasoline, diesel fuel, or natural gas in the air generally contains high levels of nitrogen, some carbon dioxide, and small amounts of oxygen, carbon monoxide, and water vapor.
The carbon dioxide and water vapor impurities are relatively inert, thus are not objectionable in many subsequent uses of the inert gas. For most applications, the oxygen level is low enough at process discharge to be used as an inert gas. If necessary, water vapor can be removed (typically, by two phase separators, adsorption, or by a membrane permeation technique).
A need exists to efficiently produce inert gases with simple on-site methods, thus avoiding high transportation costs associated with delivery to point of use locations.
A need exists to reduce the high costs associated using current on-site methodologies to generate inert gases due to high energy requirements, and to achieve higher nitrogen gas flow rates at high purity production levels without compromising safety concerns.
The embodiments meet these needs.
The present embodiments are detailed below with reference to the listed Figures.